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Physics > Electricity- Paper 1 > Flashcards

Electricity- Paper 1 Flashcards

1
Q

What is Current? 3

A

=Flow of Electrical Charge
.current only flow if a source of potential difference.
.unit of current=ampere.

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2
Q

What is the potential difference?

A

.Potential difference (voltage) pushes the charge round. unit is the volt, V.

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3
Q

What is resistance?

A

.Resistance= slows the flow down. Unit: ohm
.current flowing through component depends potential difference across=resistance of the component.
.greater resistance across a component=the smaller the current that flows

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4
Q

Total Charge Through a Circuit Depends on?

A

Current and Time

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5
Q

What is rate of flow of charge?

A

The size of the current is the rate of flow of charge.

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6
Q

Charge flow?
All the symbols? 7

A

charge flow (c)= current (a)xTime

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7
Q

Formula Linking Potential Difference and Current?

A

Potential difference (v)=current (A)xResistance (ohms)

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8
Q

Investigating the Factors Affecting Resistance? 2

A

.resistance factors: whether components are in series or parallel, length of wire.

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9
Q

Ammeter?

A

.Measures the current (in amps) flowing through the test wire, placed in series when investigating things.

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10
Q

Voltmeter?

A

Measures the potential difference across the test wire (in volts) always be placed in parallel what investigating.

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11
Q

Investigating wire length effect on resistance? 6

A

1)Attach a crocodile clip wire level with O cm on the ruler.
2)Attach the second crocodile clip to the wire 10 cm away from first clip.
3) Close the switch=record current through wire and the pd across it.
4)Open the switch, move the second crocodile clip another 10 cm. Close the switch, record new length, current,pd.
5)Repeat for a number of different lengths of the test wire.
6) calculate resistance each length wire, R = V ÷ I Plot a graph= straight line origin, resistance directly proportional length

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12
Q

What is a ohmic conductor?

A

.resistance of ohmic conductors doesn’t change with the current.
.constant temperature
.current flowing through an ohmic conductor directly proportional to pd across.

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13
Q

What is a filament lamp?

A

1)electrical charge flows through filament lamp=transfers some energy= thermal energy store
2)filament heat up. Resistance increases temp= current increases

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14
Q

What is a diode?

A

.resistance depends direction of the current.
- current flow in one direction, but have a very high resistance if reversed.

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15
Q

Method experiment to find a component’s /-V characteristic?

A

1) set up the circuit vary the variable resistor. Alters current flowing +PD
2) Multiple readings ammeter voltmeter PD across component varies current changes. Repeat each reading twice average pd each current.
3) Swap wires connected to the battery= direction of the current is reversed.
4) Plot a graph of current against voltage for the component.
5) The I-V characteristics you get for an ohmic conductor, filament lamp and diode should look like this:

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16
Q

Graphs for ohmic conductor, filament lamp and diode graph?

A
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17
Q

What is a Light Dependent Resistor?

A
  • resistor that is dependent on the intensity of light.
    1) bright light, the resistance falls. In darkness, the resistance is highest.
    2) night lights, outdoor lighting and burglar detectors.
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18
Q

What is a Thermistor?

A

A thermistor is a temperature dependent resistor. Can be used temperature detectors
.In hot conditions, the resistance drops. In cool conditions, the resistance goes up.

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19
Q

how can you use Thermistors in what circuit?

A

.Sensing circuits can be used to turn on/increase the power components depending on the conditions that they are in.
1) fixed resistor fan will always have the same potential difference across them (parallel).
2) power supply is shared out thermistor + loop made up fixed resistor, fan according resistances=bigger component’s resistance, more pd it takes.
3) gets hotter, resistance thermistor decreases, takes a smaller share of pd from power supply. pd across the fixed resistor, the fan rises= fan faster.

.can also connect the component across the variable resistor instead

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20
Q

LDRs and Thermistors graph shape light intensity?

A
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21
Q

Series Circuits? 2

A

1)different components connected line of power supply (except voltmeters, connected in parallel).
2)disconnect one component=circuit broken all stop.

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22
Q

Series Circuits Potential Difference? 2

A

.total pd of the supply is shared between various components.
.Pd series circuit add up to equal the source pd

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23
Q

Series circuit Current?
What is this determined by? 2

A

. same current flows through all components,
-size of the current is determined by the total pd of the cells and the total resistance circuit: I= V ÷ R

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24
Q

Series circuit Resistance? 2

A

.total resistance=two resistors have to share the total pd.
.total resistance is lower then r1 and r2

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25
Q

Series Cell Potential Differences?

A

=bigger pd when more cells are in series, if they’re all connected the same way.
.For example when two cells with a potential difference of 1.5 V are connected in series they supply 3 V between them.

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26
Q

Parallel Circuits? 2

A

.each component separately connected to power (except ammeters, always connected in series).
=Remove or disconnect one of them, no effect. able to switch everything on+off separately. Car lights

27
Q

Parallel Circuits Potential Difference?

A

.all components get full source pd all same (identical bulbs connected in parallel=same brightness.)

28
Q

Parallel Circuits Current?

A

.total current flowing=to total of all currents through separate components.
.junctions current either splits or rejoins.
Total current= I1+I2

29
Q

Parallel Circuits Resistor?

A

.two resistors in parallel=total resistance less than the resistance of smallest two resistors (both resistors same PD across them as the source)
.’pushing force’ making current flow is pd for each resistor that you add, adding another loop, current has more than one direction to go in.
=increases the total current that can flow around the circuit. (V = IR)
Increase in current= decrease in the total resistance circuit.

30
Q

How to investigate Adding Resistors in Series? 4

A

1) Four identical resistors, circuit shown on the right using one of the resistors. Note PD of battery (V).
2)Measure current through the circuit using ammeter (calculate resistance R= V ÷I) Add resistor, in series with the first.
3)measure current through the circuit and use this and the PD of the battery to calculate overall resistance of the circuit.
4)Repeat steps 3 and 4 until you’ve added all of your resistors. (Plot a graph number resistors against total resistance circuit)

31
Q

How to investigate adding resistors in parallel? 3

A

1) Measure total current through circuit + calculate resistance of circuit using R = V ÷ I, V (PD of the battery.)
2)add another resistor, in parallel with the first.Measure total current through circuit use and PD battery calculate overall resistance circuit.
3)Repeat steps 1,2 until you’ve added all Resistors. (Plot a graph number of resistors in the circuit against the total resistance)

32
Q

Resistance Rules? Parrel and series

A

.adding resistors series Increases total resistance of the circuit (decreases overall current circuit.)
=more resistors you add, the larger resistance whole circuit.

.add resistors parallel, total current through circuit increases -total resistance circuit has decreased. More resistors you add, smaller overall resistance becomes

33
Q

Parallel of resistance and identical resistors?

A
34
Q

Series of resistance and identical resistors?

A
35
Q

What is alternating current (ac)?

A

.current constantly changing direction. Alternating currents produced by alternating voltage, positive and negative ends keep alternating.
.UK mains supply is an ac supply

36
Q

What is direct current (dc)?

A

.cells and batteries supply direct current (dc). current that is always flowing in the same direction. created by a direct voltage.

37
Q

Mains supply voltage and frequency?

A

. 230 V. frequency 50 Hz (hertz). In AC

38
Q

Brown wire?

A

.live wire provides the alternating potential difference (230 V) from the mains supply.

39
Q

Blue wire?

A

.neutral wire completes circuit - appliance is operating normally, current flows through the live and neutral wires.

40
Q

green and yellow wire?

A

.protecting the wiring, and for safety - stops the appliance casing from becoming live. It doesn’t carry a current - only when there’s a fault. Earth wire

41
Q

Why The Live Wire Can Give You an Electric Shock?

A

Your body low resistance = you touch the live wire, a large PD is produced across body, current flows through you.= electric shock
(earthed)

42
Q

Why does a plug still shock you when it’s turned off?

A

.current isn’t flowing but there’s still a pd in the live wire.=body would provide a link between supply and earth, current flow through you.

43
Q

Why is a connection with live and earth wire dangerous?

A

.link creates a low resistance path to earth, a huge current will flow, result in a fire.

44
Q

How Energy is Transferred from Cells and Other Sources?

A

.charge transfer energy against resistance of the circuit.
.Electrical appliances transfer energy components in circuit when a current flows.

45
Q

How does a kettle transfer energy?

A

1)Kettles transfer energy electrically mains ac supply to thermal energy store heating element inside the kettle.

46
Q

Does all energy get transferred usefully any factors?

A

No. higher the current, more energy is transferred to thermal energy stores of components.
You can calculate the efficiency of any electrical appliance: energy transferred (j)= power (w)x Time (s)

47
Q

1)Why does Energy Transferred Depends on the Power?
2)What is power?

A

1)total energy transferred by appliance depends how long the appliance is on for=power.
2)power of appliance= energy that it transfers per second

Energy transferred(J)= charge flow(c)x PD(V)

48
Q

Why use a Power rating?

A

. power rating - they’re labelled with the maximum safe power operate at. (maximum amount of energy transferred between stores per second)
.helps customers choose between models – lower power=cheaper to run

49
Q

Why is a high power not always good?

A

.less efficient only transfer the same amount of energy (or even less) to useful stores.

50
Q

Why is Potential Difference Energy Transferred per Charge Passed?

A

.electrical charge goes change in potential difference, then energy is transferred.
.Energy is supplied to the charge at the power source ‘raise’ it through a potential.
.charge gives up this energy when it ‘falls’ through any potential drop in components elsewhere in the circuit.

. battery with a bigger pd will supply more energy to the circuit every coulomb of charge which flows round it,charge is raised up “higher” at the start.

Power (w)=PD(v)x current (a)

51
Q

What else does Power Also Depends on? 2

A

.Current and Potential Difference:
power= PDx current or Power= Current^2x resistance

52
Q

What is the national grid?

A

1)giant system of cables and transformers covers the UK connects power stations to consumers
2) The national grid transfers electrical power from power stations anywhere on the grid (the supply)

53
Q

Electricity Production Demands?

A

1) Power stations have to produce enough electricity for everyone to have it when they need it.
2) Demand increases morning, school or work.

54
Q

Why does the National Grid Uses a High Pd and a Low Current?

A

.transmit the huge amount of power needed, you need either a high potential difference or a high current
.high current=lose loads of energy as the wires heat up energy is transferred thermal. cheaper to boost the pd, keep the current as possible.

55
Q

Why us Potential Difference is Changed by a Transformer?

A

=get the voltage up for efficient transmission use transformers.
=Potential difference (p) is increased using a step-up transformer. step-down transformer reduced

56
Q

How does a transformer work? 4

A

1)Transformers two coils, a primary coil and secondary coil, iron core.
2)step up more turns on the secondary coil than the primary coil. pd is increased by the transformer, the current is decreased.
3)pd reduced again local consumer step-down transformer (current increased). more turns primary coil than the secondary.
4) Transformers 100% efficient, power in primary coil = power in secondary coil.

57
Q

Build-up of Static is Caused by Friction but why and how are they moved? 2

A

1)insulating materials are rubbed together, negatively charged electrons scraped off one and dumped on the other.
2)materials electrically charged, positive static charge on one and an equal negative static charge on the other.
.Which way the electrons are transferred depends on the two materials involved.

58
Q

Why do Only Electrons Move - Never Positive Charges?

A

.Both +ve and -ve electrostatic charges only produced by the movement of electrons. positive charges do not move!
.positive static charge caused by electrons moving away elsewhere.
.material that loses electrons loses some negative charge=equal positive charge.

59
Q

Why does Too Much Static Causes Sparks?

A

1.electric charge builds on object, PD between object+earth increases.=large enough, electrons jump across gap between charged object and earth= spark.
2.jump to earthed conductor nearby=static shocks getting out car. charge builds up car’s metal frame, touch car, charge travels through you to earth

60
Q

Why do Charges Repel?

A

Opposite Charges Attract, same repel (two electrically charged objects brought close exert a force on one another)

61
Q

What is electrostatic attraction / repulsion?

A

.forces get weaker the further apart the two things are= fore them to move (non-contact force)

62
Q

Why do Electric Charges Create an Electric Field? 3

A

1.electric field is created around electrically charged object= closer object you get, the stronger the field is.
2.show electric field around an object using field lines. (right angle surface, closer together lines are, stronger field is)
3.further from charge=further apart lines are=so the weaker the field is.

63
Q

Why do Charged Objects in an Electric Field feel a Force? 3

A

1) force=attraction or repulsion (by electric fields charged objects interacting with each other)
2) force on object=strength electric field it is in.
3)increase distance between the charged objects, strength field decrease= force between them gets smaller

64
Q

How can Sparking Be Explained By Electric Fields?

A

.caused high enough PD between a charged object earth= electric field
1) strong electric field causes electrons in the air particles to be removed (ionisation).
2) Air insulator, ionised it is more conductive=current can flow through it=spark.

Physics (12 decks)

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